# CVE-2026-74727: ovpn: skip rehash for peers already removed from by_id

> A race condition in the Linux kernel OVPN module allows a use-after-free, potentially enabling code execution or denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** BELL-CVE-2026-74727, DEBIAN-CVE-2026-74727, GHSA-vxqr-379f-fhc4, UBUNTU-CVE-2026-74727

## What is CVE-2026-74727?

CVE-2026-74727 is a critical use after free vulnerability in Linux, published on 22 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ovpn: skip rehash for peers already removed from by_id

ovpn_nl_peer_set_doit() resolves the target peer via
ovpn_peer_get_by_id() before taking ovpn->lock. In the window between
the lookup (which only takes a refcount) and the subsequent
spin_lock_bh(&ovpn->lock), a concurrent OVPN_CMD_PEER_DEL, keepalive
expiry, or socket teardown can take ovpn->lock first, run
ovpn_peer_remove() to unhash the peer from all four tables (by_id,
by_vpn_addr4/6, by_transp_addr) and release the lock. set_doit then
acquires ovpn->lock and calls ovpn_peer_hash_vpn_ip(), which
re-inserts the now-removed peer back into the rehashing tables.

The same race affects the float path: ovpn_peer_endpoints_update()
holds only a refcount and acquires ovpn->lock very late (after async
AEAD decrypt and a netlink notification), then rehashes the peer
in the by_transp_addr table.

The resurrected peer becomes reachable again from the RX lookup
(ovpn_peer_get_by_transp_addr) and the TX VPN-IP lookup, even though
userspace believes it is gone. Once the data-path refcount drops the
peer is freed via call_rcu while the hash entries embedded in it
remain linked, opening a UAF window.

Bail out of the rehash when hash_entry_id is unhashed, mirroring
the sentinel already used by ovpn_peer_remove() to detect the
already-removed state. The check is safe under ovpn->lock, which
serializes every mutation of hash_entry_id, and is a no-op for the
add path because ovpn_peer_add_mp() inserts hash_entry_id before
calling ovpn_peer_hash_vpn_ip().

## Which versions are affected by CVE-2026-74727?


## How do I fix CVE-2026-74727?

Apply the vendor's patch.

## Is CVE-2026-74727 being exploited?

There is no known exploitation of CVE-2026-74727 in the wild and no public exploit code.

Public exploit code:

- Upstream OpenVPN kernel fix for CVE-2026-74727, tested on Ubuntu kernel 7.0.0-38.38. Includes build instructions and functional test results. (github_poc): https://github.com/Kosifuchs/ovpn-kernel-backport

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74727 and fix it if it is affected.

What it is: CVE-2026-74727 is a critical use after free vulnerability in Linux, published on 22 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74727 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-74727/ (Markdown: https://insights.sbomify.com/CVE-2026-74727/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74727
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74727
- OSV: https://osv.dev/vulnerability/CVE-2026-74727

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74727/
Summaries are generated and may contain mistakes; the official description above is the record.